This invention relates to a process for the manufacture of a starch product containing at least about 15% amylase resistant starch from a starch that contains at least 40% amylose.
Starch, a complex carbohydrate, is composed of two types of polysaccharide molecules: amylose, a mostly linear and flexible polymer of D-anhydroglucose units that are linked by alpha-1,4-D-glucosidic bonds, and amylopectin, a branched polymer of amylose chains that are linked by alpha-1,6-D-glucosidic bonds. Starch is digested predominantly in the small intestine by the enzyme alpha-amylase. Alpha-amylase hydrolyzes alpha-1,4-glycosidic bonds, and therefore hydrolyzes the amylose fraction of starch almost completely to simple sugars. Alpha-amylase does not hydrolyze the alpha-1,6-D-glucosidic linkages, resulting in less complete hydrolysis of the amylopectin fraction.
It is known that certain starch processing operations result in the transformation of starch into starch that is resistant to amylase, known simply as resistant starch. Resistant starch is not digested by amylases in the small intestine, but passes into the large intestine where, research literature indicates, it behaves with properties similar to soluble and insoluble dietary fiber. Resistant starch, thus, has reduced caloric value because it resists digestion, and it is likely to be a factor in the prevention of diverticulosis and colon cancer and lowering blood cholesterol levels.
It is generally believed that resistant starch is formed when the amylose fraction of starch is retrograded or recrystallized after the gelatinization of starch. The theory is that the flexible linear amylose molecules align themselves after gelatinization into tight linear configurations that can form helices or spheres making many of the alpha-1,4-glucosidic linkages inaccessible to alpha-amylase. Normally, as described in the literature, the process for the formation of resistant starch by retrogradation is cumbersome involving the initial gelatinization and then the cooling of starch, frequently with repeated cycles.
U.S. Pat. No. 5,051,271 issued on Sep. 24 1991 to Iyengar, et al. discloses a process for preparing a food grade, insoluble bulking agent from starch involving a retrogradation followed by enzymatic or chemical hydrolysis. To prepare the insoluble bulking agent the starting starch first is dispersed in an aqueous medium and then subjected to extended incubation at temperatures down to 4.degree. C. This step is stated to transform the starch structure to double-helical crystalline regions interspersed with amorphous regions. The reference states that since the retrogradation of amylose is retarded by the presence of amylopectin in the starch, the process can be accelerated by enzymatic conversion of amylopectin to amylose prior to retrogradation by the use of debranching enzymes, such as pullulanase or isoamylase, or by partial hydrolysis with alpha-amylase. The retrograded starch is then subjected to enzymatic or acid hydrolysis to eliminate the amorphous regions and to produce a starch that is essentially free of amorphous regions and that contains at least 90% crystalline material.
This and other reported methods for preparing resistant starch call for cycles of heating and cooling, or isolation of the resistant starch by removing non-resistant materials through enzyme or chemical hydrolysis. These methods are tedious and commercially impracticable and the need remains for a commercially feasible process.